This invention relates to a system for automatically manipulating and aligning elements such as semiconductor wafers.
In many manufacturing, processing or sorting systems, controlled robots having articulated robot arms have been used to move elements such as semiconductor wafers from one processing or storage station to another. Such robots are movable in vertical (Z), horizontal (.crclbar.) and radial (r) directions and their manipulation must be done repetitively at high speed and with maximum precision and reliability. Also, in semiconductor processing when one or a series of wafers are moved sequentially from station to station, they must be placed at each station in the same predetermined orientation or alignment with respect to both the center of the wafer and also a point of reference or fiducial on the edge of the wafer. Thus, each wafer has a distinguishing point of reference such as a notch or a flat spot on its peripheral edge, and at each station or storage cassette to which the wafers are moved to or from the notches and the centers of all wafers must be in precise alignment.
Various prior art aligner devices have been devised that attempt to solve this problem. One such device described in U.S. Pat. No. 5,102,280 utilizes a robot arm which is manipulated to lift a wafer that is on a vacuum chuck and move it laterally until it becomes centered on the vacuum chuck. Thereafter, the wafer is rotated until a predetermined position on the edge of the wafer is located by a sensor. The sensor controls the rotating chuck so that it stops with the retained wafer in a preselected .crclbar. position. The robot arm is then required to move the wafer until it is centered on the chuck before it is removed therefrom. The present invention provides an improved robot apparatus and method for aligning wafers or elements with greater precision, speed and reliability.